In recent years, a light source device that employs an organic electroluminescent element (hereinafter referred to as organic EL element) is attracting attention as a type of flat light source devices. The light source device employing the organic EL element has excellent properties such as self-light emission, wide viewing angle, and high-speed response.
The organic EL element generally includes an organic layer on a transparent substrate, which organic layer includes (i) a first electrode (anode) serving as a transparent electrode, (ii) a second electrode (cathode) serving as a reflecting electrode, and (iii) a light-emitting layer between the first electrode and the second electrode. The organic layer generally includes, in addition to the light-emitting layer, a hole transport layer, an electron transport layer, and the like. Application of a voltage of a few volts between the first electrode and the second electrode in the organic EL element causes a hole injected from the first electrode and an electron injected from the second electrode to be bound to each other again in the light-emitting layer. When the hole and the electron are bound to each other again in the light-emitting layer, an exciton is generated. The exciton emits light when it returns to its ground state. In this manner, the organic EL element emits light. In an organic EL element of a bottom emission type, light emitted from the organic EL element is taken out from a side where the first electrode and the transparent substrate are provided. In contrast, in an organic EL element of a top emission type, light emitted from the organic EL element is taken out from a second electrode side.
In order for the organic EL element to be used in a light source device, the organic EL element is required to have a large area. A vacuum process, which is one of methods for manufacturing the organic EL element, does not allow a large-sized organic EL element to be manufactured easily. This is due to an enormous amount of takt time resulting from technical difficulty in manufacturing an organic EL element by use of a large-sized substrate in the vacuum process.
In addition, installing an apparatus for manufacturing the large-sized organic EL involves an enormous cost. Because of these drawbacks, in fact, there has been reported no case of an organic EL element manufactured by use of a tenth-generation substrate, which currently is the largest-sized substrate.
In order to address the problem, a method has been employed recently, in which method a large-sized light source device is manufactured by mounting a plurality of small-area organic EL elements manufactured by use of a medium-sized vacuum film formation device. The method is highly feasible for the following reasons. That is, since a glass substrate is reduced in size, (1) a light source device with a large-area light-emitting surface can be manufactured by a simple method, (2) a manufacturing method according to vacuum evaporation manufacture, development of which is currently more advanced than a wet process and therefore has an advantage of being capable of achieving high light-emitting efficiency, can be applied, (3) a fixed cost for installing a manufacturing apparatus and a takt time can be reduced since a vacuum system of the manufacturing apparatus can be made compact, and (4) so on. In particular, a light source device in which a plurality of strip-like organic EL elements are mounted is coming into increasing use as a flat light source device. This light source device is called blind-type illumination device or the like because of its shape.
Recently, a blind-type illumination device in which a light-emitting element other than the organic EL element is mounted has been developed as well. For example, Patent Literature 1 discloses a blind-type illumination device manufactured by integrating a plurality of slats, in each of which a luminous body, which emits light by utilizing electric energy generated by a solar cell, is mounted. Specifically, the blind-type illumination device disclosed in Patent Literature 1 includes the solar cell, a secondary battery, and the luminous body. The secondary battery stores electric energy generated by the solar cell, and the luminous body emits light by receiving a voltage supplied by the secondary battery. In the blind-type illumination device disclosed in Patent Literature 1, the solar cell is provided on a light-blocking surface of the slats, which are plates (blades) of the blind, and solar energy is transformed into electric energy at the time of blocking light. This allows solar energy of blocked light to be converted into electric energy so as to be utilized as illumination for a room. Thus, effective use of solar energy is realized.